AWS CDK: Infrastructure as TypeScript

CloudFormation YAML is verbose and lacks logic. The AWS Cloud Development Kit (CDK) allows you to define cloud resources using imperative languages. In this guide, we build a complete serverless stack (Lambda + API Gateway + DynamoDB) using TypeScript.

The Construct Tree

CDK components are called “Constructs”. Level 1 (L1) constructs are 1:1 mappings to CloudFormation. Level 2 (L2) constructs offer high-level abstractions with sensible defaults.

import * as cdk from '@aws-cdk/core';
import * as lambda from '@aws-cdk/aws-lambda';
import * as apigateway from '@aws-cdk/aws-apigateway';
import * as dynamodb from '@aws-cdk/aws-dynamodb';

export class ServerlessStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // L2 Construct: DynamoDB Table
    const table = new dynamodb.Table(this, 'ItemsTable', {
      partitionKey: { name: 'pk', type: dynamodb.AttributeType.STRING },
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST, // On-Demand
      removalPolicy: cdk.RemovalPolicy.DESTROY // For dev only
    });

    // L2 Construct: Lambda
    const handler = new lambda.Function(this, 'ItemHandler', {
      runtime: lambda.Runtime.NODEJS_12_X,
      code: lambda.Code.fromAsset('lambdas'),
      handler: 'items.handler',
      environment: {
        TABLE_NAME: table.tableName
      }
    });

    // Auto-grant permissions (IAM)
    table.grantReadWriteData(handler);

    // L2 Construct: API Gateway
    const api = new apigateway.RestApi(this, 'ItemsApi');
    api.root.addMethod('GET', new apigateway.LambdaIntegration(handler));
  }
}

Synthesis and Deployment

CDK compiles your code into a CloudFormation template.

# Generate YAML
cdk synth

# Deploy to AWS
cdk deploy

Testing Infrastructure

Since it’s code, you can write unit tests using `@aws-cdk/assert`.

test('DynamoDB Table Created', () => {
    const app = new cdk.App();
    const stack = new ServerlessStack(app, 'MyTestStack');
    
    expectCDK(stack).to(haveResource('AWS::DynamoDB::Table', {
        BillingMode: 'PAY_PER_REQUEST'
    }));
});

Key Takeaways

• CDK is **not** Terraform; it generates CloudFormation which AWS executes.
• Use **grant** methods (e.g., `grantReadWriteData`) to handle complex IAM policies automatically.
• Unit test your infrastructure configuration to catch compliance issues early.